Fe141 spirometer

Middle cerebral artery blood velocity was continuously measured using bilateral TCD ultrasound probes (2 MHz pulsed‐wave Robotic TCD probe, Neurovision, Multigon Industries). Both the left and right MCA were insonated according to previously published guidelines (Aaslid et al., 1982 (link); Willie et al., 2011 (link)). Infrared finger photoplethysmography (Human NIBP Nano System, ADInstruments) was used for continuous measurement of mean arterial pressure (MAP) with in‐software calculations for estimates of cardiac output (Q), stroke volume (SV), and total peripheral resistance (TPR). Heart rate (HR) was continuously recorded using a wireless ECG vest (EQ02 + SEM, Equivital). Pulmonary gases and flow were continuously analyzed (Gemini End‐Tidal O₂ and CO₂ Analyzer, CWE Inc.; MLT3813H Pneumotach, ADInstrumetns; FE141 Spirometer, ADInstruments) for breath‐by‐breath analysis of VO₂ and EtCO₂. All data were acquired via PowerLab (PowerLab/16SP ML 880, ADInstruments) at 20 kHz recorded using LabChart software (ADInstruments).

Subjects were examined in the supine position, in a quiet room, using a one-way open breathing circuit with remotely controlled mechanical valve attached to the inspiratory arm, which allowed for silent switching between room air, 100% oxygen or 100% nitrogen. The expiratory arm was connected via a 1000 L min⁻¹ flowhead (MLT3000L, ADInstruments) to a differential pressure transducer (FE141 Spirometer, ADInstruments) for the assessment of VI. Measured Hemodynamic parameters included: HR, CO, SVR and MAP, which were recorded non-invasively, beat-by-beat using Nexfin Finapres technique (Nexfin BMEYE B.V.). Monitor was appropriately calibrated before the test using physiological calibration. SpO₂ was evaluated using a pulse oximeter (Radical-7, Masimo Corporation Irvine) with an ear clip. SpO₂ recording was shifted backward by 15 s to compensate the circulatory delay. ETCO₂ was monitored with a CO₂ analyzer attached to the expiratory arm of the circuit (CapStar 100, CWE).